A metering device according to the above preamble is, for example, disclosed in U.S. Pat. No. 5,542,450. With this device, fluids and especially fuels can be metered accurately. Use is made of a solid block which serves as a manifold and which includes an internal filter assembly, an internal check valve, channels within the block serving as fluid conduits, and inlet and outlet ports which provide a means for connecting the block to the source of the fluid to be measured.
Although the metering device according to this U.S. patent may be provided with additional channels present in the block for the use of accessories such as pressure detectors, pressure release valves, etc., the known metering device is still a passive component as it only is capable of measuring the fluid passing through the channels in the block.
It is therefore an object of the invention to provide a metering device as described above with an additional functionality, which will improve the accuracy of the metering device during use.
According to the invention, the metering device is characterized in that a calibration valve assembly is accommodated within a channel section of said channel between the fluid outlet and the fluid meter, said calibration valve assembly being operable between a first, ‘normal’ position allowing the passage of fluid from the fluid meter towards the fluid outlet and a second, ‘calibration’ position blocking the passage of fluid from the fluid meter towards the fluid outlet.
With this calibration functionality it is possible to set the device in a so called calibration cycle improving the accuracy and functionality of the device.
In a further embodiment in the second, ‘calibration’ position said calibration valve assembly is in fluid connection with a calibration channel present within said block. This allows an accurate calibration of the metering device wherein no fluid is spilled or leaking out of the channels present in the block allowing a highly accurate calibration step also with the use of very small fluid quantities.
In a specific embodiment, the calibration valve assembly comprises a valve spindle to be rotatably mounted within said channel, said valve spindle having a bore, which bore can be brought in fluid communication with said channel and said fluid outlet or said calibration channel upon rotating said valve spindle between said first and second positions and vice versa. With these technical features, it is possible to set the metering device in an accurate and an unambiguous way from its normal operation position towards its calibration position
Furthermore, the outer dimensions of said valve spindle conform to the inner dimensions of said channel section.
Moreover, as the valve spindle has outer dimensions which conform to the inner dimensions of the channel section within the block, no leakage will occur and no fluid to be metered will leak away towards the normal outlet but will be maintained within the calibration channel, allowing for an accurate calibration step.
In order to set the flow rate of the fluid through the metering device accurately a valve stem is mounted within the bore of said valve spindle and arranged in setting the flow rate through the bore.
Especially the valve stem is provided with an outer screw thread engaging an inner screw thread provided in the inner circumferential surface of the bore, so to allow an accurate setting of the valve stem within the valve spindle and hence an accurate flow rate setting.